Fiberizable alkali-resistant E-type glass

ABSTRACT

Glass compositions consisting essentially of an E-glass are modified by incorporation therein of zirconia or of zirconia and titania, preferably in a total amount not exceeding 12%, more preferably not exceeding 8%, by weight of the composition, whereby significant improvement in alkali resistance is achieved.

This application is a continuation of our earlier application Ser. No. 450,231 filed Mar. 11, 1974, now abandoned.

This invention concerns improvements in or relating to glass compositions and fibres made therefrom.

Attempts to use E-glass as a reinforcement in cementitious products in the building industry have been essentially unsuccessful, since the high alkalinity of the hydrated cement matrix degrades the fibres and the advantages of reinforcing with such fibres therefore markedly diminishes with time.

An object of the present invention is to obviate or mitigate the above disadvantages.

The present invention provides a glass composition consisting of an E-glass modified with additions of zirconia or zirconia and titania in proportions such as to impart improved alkali resistance (i.e. improved over that exhibited by unmodified E-glass) but below such proportions at which crystal nucleation interferes with a melt drawing process.

It is a matter of simple experimental test to determine the concentration of titania and/or zirconia at which crystal nucleation occurs.

The proportion of titania added preferably is within the range from 1 to 6% by weight of the total glass composition; the proportion of zirconia added preferably is within the range from 2 to 6% by weight of the total glass composition; and the total weight of titania and zirconia added to the composition preferably does not exceed 8% by weight of the total glass composition.

Less preferably, because devitrification may occur at the higher proportions, the TiO₂ may be present in an amount up to 8% by weight and the TiO₂ and ZrO₂ together may be present in an amount up to 12% by weight of the composition.

Glass according to the invention may thus consist essentially of:

    SiO.sub.2  46 to 56% (by weight)                                               B.sub.2 O.sub.3                                                                            6 to 12%                                                           R.sub.2 O.sub.3                                                                           12 to 17% (Fe.sub.2 O.sub.3 less than 1%)                           CaO        13 to 24%                                                           MgO         0 to  6%                                                           F           0 to  1%                                                           R.sub.2 O  less than 1%                                                        ZrO.sub.2   2 to  6%                                                           TiO.sub.2   0 to  6%                                                      

R₂ O₃ is Al₂ O₃ and Fe₂ O₃ with minor amounts of similar oxides, and R₂ O is Li₂ O, Na₂ O or K₂ O or a mixture of at least two thereof; R₂ O is usually present, if at all, as impurity, as is F. The total percentage of CaO plus MgO should not exceed 25%.

The zirconia can be added in the form of zircon (zirconium silicate).

It is found that glasses according to this invention possess good melt drawing properties as a result of the presence of the minor components in E-glass, such as boric oxide, which are responsible for the good melt drawing properties of E-glass, so that the efficiency of the melt drawing apparatus (when used for compositions according to this invention) is far superior to that obtained from simple glasses.

Preferred embodiments of the present invention will now be described, for the purposes of illustration, in the following Examples.

EXAMPLE 1

A glass of the following composition was made and was melt drawn at 1210°C, percentages being by weight of the total composition:

    Silica          48.70%                                                         Alumina         13.25%                                                         Calcium Oxide   15.50%      Typical                                            Magnesium Oxide  4.80%      E-glass                                            Boric Oxide      9.75%                                                         Titania          4.0%                                                          Zirconia         4.0%                                                     

The fibres obtained exhibited a tensile strength of 0.91 GPa (GPa = GN/m²) after treatment in boiling saturated calcium hydroxide, followed by washes in distilled water, 1% HCl acid for one minute, water and acetone and final drying.

The fibres retained approximately 65% of the original strength, whereas the unmodified E-glass retained only approximately 35% of its original strength after the same treatment.

EXAMPLE 2

Fibres were produced, as in Example 1, with the following composition:SiO₂ 52.3%B₂ O₃ 7.3% TypicalAl₂ O₃ 13.3% E-GlassFe₂ O₃ 0.4%CaO 18.2%MgO 3.6%Na₂ O 0.2% TypicalK₂ O 0.7% E-glassZrO₂ 4.0%

Before the alkali treatment the strengths of the unmodified (no zirconia) E-glass and the ZrO₂ -modified E-glass were 0.93 GPa and 1.15 Pa respectively, whereas after alkali-treatment, the strengths were 0.36 and 0.65 respectively, showing strength retention of about 35% for the unmodified E-glass as against about 56% for the modified composition.

EXAMPLE 3

Fibres were produced, as in Example 1, with the following composition:

    SiO.sub.2     51.3%                                                            B.sub.2 O.sub.3                                                                               7.0%                                                            Al.sub.2 O.sub.3                                                                             13.0%      Same E-glass as                                       Fe.sub.2 O.sub.3                                                                              0.4%      in Example 2                                          CaO           17.9%                                                            MgO            3.5%                                                            Na.sub.2 O     0.2%                                                            K.sub.2 O      0.7%                                                            ZrO.sub.2      6.0%                                                       

After alkali treatment, this glass had a strength of 0.62 GPa, or a strength retention of about 54%.

It can be seen that the degree of alkali resistance may thus be varied and improved by adjusting the proportions of titania and zirconia within the ranges specified above. 

We claim:
 1. A fiberizable glass composition exhibiting improved alkali resistance consisting essentially, by weight, of

    SiO.sub.2  46 to 56%                                                           B.sub.2 O.sub.3                                                                            7 to 12%                                                           R.sub.2 O.sub.3                                                                           12 to 17% (Fe.sub.2 O.sub.3 less than 1%)                           CaO        13 to 24%                                                           MgO         0 to 6%                                                            F           0 to 1%                                                            R.sub.2 O  less than 1%                                                        ZrO.sub.2   2 to 6%                                                            TiO.sub.2   0 to 6%                                                       

wherein R₂ O₃ is Al₂ O₃ with less than 1% Fe₂ O₃ and minor amounts of similar oxides, and R₂ O is Li₂ O, Na₂ O, K₂ O or a mixture of at least two thereof, said glass composition having improved alkali resistance compared to a similar composition absent titania and zirconia, wherein CaO plus MgO does not exceed 25%, and ZrO₂ plus TiO₂ does not exceed 8%.
 2. A glass composition according to claim 1, consisting essentially of:

    SiO           48.70%                                                           Al.sub.2 O.sub.3                                                                             13.25%                                                           CaO           15.50%                                                           MgO            4.80%                                                           B.sub.2 O.sub.3                                                                               9.75%                                                           TiO.sub.2      4.00%                                                           ZrO.sub.2      4.00%.                                                     


3. A glass composition according to claim 1, consisting essentially of:

    SiO.sub.2     52.3%                                                            B.sub.2 O.sub.3                                                                               7.3%                                                            Al.sub.2 O.sub.3                                                                             13.3%                                                            Fe.sub.2 O.sub.3                                                                              0.4%                                                            CaO           18.2%                                                            MgO            3.6%                                                            Na.sub.2 O     0.2%                                                            K.sub.2 O      0.7%                                                            ZrO.sub.2      4.0%.                                                      


4. A glass composition according to claim 1 consisting essentially of:

    SiO.sub.2     51.3%                                                            B.sub.2 O.sub.3                                                                               7.0%                                                            Al.sub.2 O.sub.3                                                                             13.0%                                                            Fe.sub.2 O.sub.3                                                                              0.4%                                                            CaO           17.9%                                                            MgO            3.5%                                                            Na.sub.2 O     0.2%                                                            K.sub.2 O      0.7%                                                            ZrO.sub.2      6.0%.                                                      


5. A process for improving the alkali resistance of a fiberizable glass composition consisting essentially of:

    SiO.sub.2  46 to 56%                                                           B.sub.2 O.sub.3                                                                            7 to 12%                                                           R.sub.2 O.sub.3                                                                           12 to 17%                                                                      (Fe.sub.2 O.sub.3 less than 1%)                                     CaO        13 to 24%                                                           MgO         0 to 6%                                                            F           0 to 1%                                                            R.sub.2 O  less than 1%                                                   

comprising adding to said glass composition from 2 to 6% ZrO₂ and optionally from 0 to 6% TiO₂, the percentages being by weight of the final composition, wherein R₂ O₃ is Al₂ O₃ with less than 1% Fe₂ O₃ and minor amounts of similar oxides, and R₂ O is Li₂ O, Na₂ O, K₂ O or a mixture of at least two thereof, the resulting glass composition exhibiting improved alkali resistance compared to a similar composition absent the titania and/or zirconia, wherein CaO plus MgO does not exceed 25%, and ZrO₂ plus TiO₂ does not exceed 8%.
 6. The process of claim 5 wherein during the addition the B₂ O₃ content of the product is maintained at 7% or more and the R₂ O content is maintained below 1%. 